Check citizenship documentation first: a current passport or citizenship certificate showing the applicant's actual citizenship status. Only once that confirms Canadian or Mexican citizenship does it make sense to move on to profession-specific or employer documentation.
Confirm citizenship before anything profession-specific
Avoid ordering credential evaluations, translations, or employer letters tailored to a TN filing until citizenship eligibility is confirmed, since none of that preparation applies if the applicant does not hold qualifying citizenship. If Canadian citizenship is pending, ask what documentation exists showing the expected completion date, since that affects the realistic timeline more than any TN-specific paperwork would. Order nothing profession-specific until the threshold is settled.
The only document worth obtaining first is the one proving citizenship: a current passport or citizenship certificate. Credential evaluations, translations, and employer letters tailored to this route have no value if the applicant does not hold qualifying citizenship, and they rarely transfer cleanly to a different route with different requirements. Where Canadian citizenship is pending, ask what documentation exists showing the application's stage and any expected timescale, since that affects planning far more than any packet of professional evidence would.
Keep the citizenship documents together with a note of what was checked and on what date, so the point is not revisited.